Here's something the well-educated woman can stop worrying about: That she will somehow increase her risk of divorce by marrying a less-educated man.

That used to be true, but it no longer is, according to a new study. Researchers say it's the latest sign that heterosexual marriages in the United States are becoming less bound by traditional gender expectations.

It's also a sign that couples are embracing a new normal, as women's education outstrips men's and such marriages become more common, says lead author Christine Schwartz, an associate professor of sociology at the University of Wisconsin-Madison.

"It's a big social change," and the fact that it does not seem to be making marriages less stable ought to dispel "a lot of fear and anxiety," Schwartz says.

The study, in the August issue of the American Sociological Review, looks at marriages formed between 1950 and 2004. It finds that marriages between educational equals have remained most common, but that when there is a difference, women are increasingly likely to have the educational edge.

In about half of marriages begun in the early 2000s, spouses had roughly equal educations. In nearly 30%, the wife had more and in about 20%, the husband had more — a reversal of the pattern seen in the 1950s through at least the late 1970s.

In those earlier eras, marriages in which wives were more educated were less likely to last. Researchers have theorized that was partly because less-educated men felt threatened by their wives' successes. It's also possible that those couples were especially non-traditional types more prone to divorce for all sorts of reasons.

But such couples married since the 1990s have had no higher divorce rates than other couples, the new study shows. They may even be less likely to divorce than couples in which men are more educated. The data is not clear on that point, researchers say.

The data does clearly show that educationally equal couples married in recent years have been less likely to divorce than those in which men are more educated, Schwartz says.

The findings are the latest to suggest that many couples are throwing out an old script that said a man had to "earn more than the woman, know more than the woman, be stronger, older, taller and wiser than the woman," says Stephanie Coontz, a professor of history and family studies at Evergreen State College in Olympia, Wash.

"We are seeing on a great many fronts a greater comfort among men with women who are their equals or perhaps even know more than they do," Coontz says. Many women also are getting more comfortable with men who may earn less or have less education, she says.

Still, "there's plenty of evidence that we have a very long way to go," toward equality and flexibility in marriage, says Veronica Tichenor, an associate professor of sociology at State University of New York Institute of Technology at Utica/Rome.

Husbands still tend to make more money than wives and wives tend to do more unpaid work at home, she says. She says wives who have more education or income than their husbands may even feel extra pressure to fill traditional roles at home, not only to please their husbands but to conform to slow-to-change cultural expectations.

"There's still this sense that men should be providers and women should be caregivers, even if they do other things too," Tichenor says.